Battery and method of manufacturing same

ABSTRACT

A battery case includes a case-penetrating hole. An external terminal includes a member-engaging hole and is stacked on an outside of the battery case so that the member-engaging hole and the case-penetrating hole align with each other. An internal terminal includes a shaft portion and a fastening portion. The shaft portion is inserted through the case-penetrating hole and the member-engaging hole from an interior of the battery. The fastening portion is fastened to a circumferential periphery of the member-engaging hole by crushing a tip end of the shaft portion. The internal terminal is stacked on an inside of the battery case. The fastening portion and the external terminal include a welded portion welded along a weld line set across a periphery of the fastening portion. The welded portion has a length K1 along the weld line and a width K2 along a direction perpendicular to the weld line, and the length K1 is at least 1.5 times longer than the width K2.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent ApplicationNo. 2018-197011 filed on Oct. 18, 2018, which is incorporated byreference herein in its entirety.

BACKGROUND

The present disclosure relates to a battery and a method ofmanufacturing the battery.

PCT/International Publication No. WO 2013/031669 discloses a battery inwhich an internal terminal is joined by riveting and an outer peripheralportion of the joined part is additionally welded. The publicationdescribes that this enables the joined part between the internalterminal and an external terminal to provide increased reliability andreduce the internal resistance.

SUMMARY

However, when the internal terminal and the external terminal are weldedtogether by spot welding, as described in WO 2013/031669, the thicknessof the weld spot will vary from one location to another. This means thatwhen the weld area is small, the electrical resistance in the joinedpart increases, resulting in a higher battery internal resistance. Forthis reason, it is necessary to provide a large weld area in order toreduce the electrical resistance in the joined part and to thereby lowerthe battery internal resistance.

A battery according to the present disclosure includes a battery case,an external terminal, and an internal terminal. The battery caseincludes a case-penetrating hole. The external terminal includes amember-engaging hole and is stacked on an outside of the battery case sothat the member-engaging hole and the case-penetrating hole align witheach other. The internal terminal is stacked on an inside of the batterycase, and includes a shaft portion and a fastening portion. The shaftportion is inserted through the case-penetrating hole and themember-engaging hole from an interior of the battery. The fasteningportion is fastened to a circumferential periphery of themember-engaging hole at a tip end of the shaft portion. The fasteningportion and the external terminal include a welded portion welded alonga weld line set across a periphery of the fastening portion. The weldedportion has a length K1 along the weld line and a width K2 along adirection perpendicular to the weld line, and the length K1 is at least1.5 times longer than the width K2. The above-described embodiment ofthe battery makes it possible to reduce the internal resistance of thebattery.

It is possible that a portion of the weld line that is provided externalto the fastening portion may be at least 1.5 times longer than a portionof the weld line that is provided internal to the fastening portion.With the above-described embodiment of the battery, the weld area can beincreased, and therefore, the internal resistance of the battery can bereduced.

Herein, the at least one welded portion may include at least two or moreof the welded portions, and adjacent ones of the welded portions may becircumferentially spaced from each other. The above-described embodimentof the battery makes it possible to further reduce the electricalresistance.

Herein, the welded portion may include an inner edge of the fasteningportion, and the inner edge may be located radially outward of themember-engaging hole when viewed axially along the shaft portion. Withthe above-described embodiment of the battery, the fastened portion isunlikely to be adversely affected by welding.

According to the present disclosure, an embodiment of the method ofmanufacturing a battery includes the steps of: preparing a battery caseincluding a case-penetrating hole; preparing an external terminalincluding a member-engaging hole; preparing an internal terminalincluding a shaft portion; assembling the battery case, the externalterminal, and the internal terminal together so that the externalterminal is stacked on an outside of the battery case, the internalterminal is stacked on an inside of the battery case, and the shaftportion is inserted through the case-penetrating hole and themember-engaging hole; forming a fastening portion by crushing a tip endof the shaft portion and fastening the tip end of the shaft portion to acircumferential periphery of the member-engaging hole on an outside ofthe external terminal; and laser welding the fastening portion and theexternal terminal seamlessly along at least one weld line that is set soas to extend across a periphery of the fastening portion along an outersurface of the fastening portion. The above-described embodiment of themethod of manufacturing a battery makes it possible to reduce theinternal resistance of the battery.

Herein, in the step of laser welding, a region external to the fasteningportion may be laser welded at least 2.5 times longer than a regioninternal to the fastening portion along the at least one weld line. Theabove-described embodiment of the method of manufacturing a batteryserves to prevent the external terminal from cracking.

Herein, in the step of laser welding, the at least one weld line may beset at two or more locations of the fastening portion that arecircumferentially spaced from each other, the fastening portion and theexternal terminal may be laser welded together along a plurality of theweld lines, and a plurality of welded portions that arecircumferentially spaced from each other may be formed by the laserwelding. The above-described embodiment of the method of manufacturing abattery serves to reduce the weld defects resulting from the occurrenceof spatter.

Herein, in the step of laser welding, the welded portion may not extendinto an inside of the member-engaging hole when viewed axially along theshaft portion. With the above-described embodiment of the method ofmanufacturing a battery, the fastened portion is unlikely to beadversely affected by welding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a battery according to anembodiment of the present disclosure.

FIG. 2 is a cross-sectional view illustrating a portion where anexternal terminal and an internal terminal are fitted to a battery case,according to an embodiment of the present disclosure.

FIG. 3 is a partial plan view illustrating a welded portion formed in afastening portion of the internal terminal and the external terminal,according to an embodiment of the present disclosure.

FIG. 4 is a cross-sectional view taken along line Iv-Iv in FIG. 3,showing a fastening portion 15 c 1.

FIG. 5 is a partial plan view illustrating a welded portion formed inthe fastening portion of the internal terminal and the externalterminal, according to a modified embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinbelow, preferred embodiments of the present invention will bedescribed. It should be noted that the following embodiments are merelyillustrative of the present invention and the present invention is notlimited to the following embodiments. The drawings are schematicillustrations, and do not necessarily reflect any actual product.

FIG. 1 is a partial cross-sectional view of a battery 10 according toone embodiment of the present disclosure. FIG. 1 depicts the interior ofthe battery 10 that is exposed along one wide side surface of a batterycase 11 in substantially a rectangular parallelepiped shape. FIG. 2 is across-sectional view illustrating a portion where an external terminal14 and an internal terminal 15 are fitted to a battery case 11. Asillustrated in FIGS. 1 and 2, the battery 10 includes the battery case11, insulating members 12 and 13, external terminals 14, internalterminals 15, and an electrode assembly 16.

Here, as illustrated in FIG. 1, the external terminals 14 and theinternal terminals 15 are fitted to the battery case 11 with theinsulating members 12 and 13 interposed therebetween. The battery case11 encloses the electrode assembly 16 and an electrolyte solution, whichis not shown. The electrode assembly 16 is covered with an insulatingfilm or the like, which is not shown, and is enclosed in the batterycase 11. Thus, the battery case 11 and the electrode assembly 16 areinsulated from each other. The electrode assembly 16 includes a positiveelectrode element, a negative electrode element, and a separator of thebattery 10.

In the present embodiment, a long sheet-shaped positive electrode sheet21 and a long sheet-shaped negative electrode sheet 22 are stacked withtwo long sheet-shaped separator sheets 31 and 32 alternately interposedbetween them, and the positive electrode sheet 21, the negativeelectrode sheet 22, and the separator sheets 31 and 32 are woundtogether to form the electrode assembly 16.

The positive electrode sheet 21 includes a positive electrode currentcollector foil 21 a having a predetermined width and a predeterminedthickness, a positive electrode active material layer 21 b containing apositive electrode active material, and an uncoated portion 21 a 1defined along one lateral edge of the positive electrode currentcollector foil 21 a with a constant width. The positive electrode activematerial layer 21 b is formed on both faces of the positive electrodecurrent collector foil 21 a, except for the uncoated portion 21 a 1. Ina lithium-ion secondary battery, for example, the positive electrodeactive material is a material that is capable of releasing lithium ionsduring charge and absorbing lithium ions during discharge, such as alithium-transition metal composite oxide. Other than thelithium-transition metal composite oxide, various materials have beenproposed for use as the positive electrode active material, and thepositive electrode active material is not limited to a particularmaterial.

The negative electrode sheet 22 includes a negative electrode currentcollector foil 22 a having a predetermined width and a predeterminedthickness, a negative electrode active material layer 22 b containing anegative electrode active material, and an uncoated portion 22 a 1defined along one lateral edge of the negative electrode currentcollector foil 22 a with a constant width. The negative electrode activematerial layer 22 b is formed on both faces of the negative electrodecurrent collector foil 22 a, except for the uncoated portion 22 a 1. Ina lithium-ion secondary battery, for example, the negative electrodeactive material is a material that is capable of absorbing lithium ionsduring charge and releasing the absorbed lithium ions during discharge,such as graphite. Other than graphite, various materials have beenproposed for use as the negative electrode active material, and thenegative electrode active material is not limited to a particularmaterial.

Each of the separator sheets 31 and 32 may be formed of, for example, anelectrolyte permeable porous resin sheet that has required heatresistance. Various proposals have been made about the separator sheets31 and 32, and there is no particular restriction on the separatorsheets 31 and 32.

The electrode assembly 16 is deformed into a flat shape pressed in onedirection perpendicular to the winding axis and is enclosed in thebattery case 11. Herein, the battery case 11 includes a case main body11 a and a lid 11 b. The case main body 11 a has a flat prismatichousing region, and one side end thereof is open. The lid 11 b has ashape corresponding to the opening of the case main body 11 a.

In the electrode assembly 16, the uncoated portion 21 a 1 of thepositive electrode sheet 21 and the uncoated portion 22 a 1 of thenegative electrode sheet 22 protrude laterally in opposite directionsfrom the separators sheets 31 and 32. The uncoated portion 21 a 1 of thepositive electrode current collector foil 21 a and the uncoated portion22 a 1 of the negative electrode current collector foil 22 a areconnected to respective internal terminals 15, which are respectivelyattached to opposite side portions of the battery case 11. The electrodeassembly 16 is enclosed in the flat internal space of the case main body11 a. After the electrode assembly 16 is placed therein, the case mainbody 11 a is closed by the lid 11 b.

In the present embodiment, as illustrated in FIG. 1, the externalterminal 14 and the internal terminal 15 are fitted to each oflongitudinally opposite side end portions of the lid 11 b. Herein, eachof the internal terminals 15 includes a base portion 15 a, an attachmentpiece 15 b, and a shaft portion 15 c. The base portion 15 a is fitted tothe lid 11 b with an insulating member 12 interposed therebetween. Theattachment piece 15 b extends from the base portion 15 a into theinterior of the battery case 11. Referring to FIG. 1, the attachmentpiece 15 b of the internal terminal 15 that is shown on the left side ofthe figure is welded to the uncoated portion 21 a 1 of the positiveelectrode current collector foil 21 a of the electrode assembly 16. Theattachment piece 15 b of the internal terminal 15 that is shown on theright side of the figure is welded to the uncoated portion 22 a 1 of thenegative electrode current collector foil 22 a of the electrode assembly16. On the outside of the lid 11 b, the external terminal 14 that isshown on the left side is fitted to a positive electrode connectingterminal 41. The external terminal 14 that is shown on the right side isfitted to a negative electrode connecting terminal 42.

As illustrated in FIG. 2, the lid 11 b includes a case-penetrating hole11 c for mounting the external terminal 14 and the internal terminal 15.In addition, a recess 11 b 1 is formed in an outer surface of the lid 11b at a position at which an insulating member 13 for insulating theexternal terminal 14 is to be fitted. The same structure is alsoprovided on the negative electrode side of the lid 11 to which theexternal terminal 14 and the internal terminal 15 are fitted. On thepositive electrode side, the external terminal 14, the internal terminal15, and the connecting terminal 41 are made of aluminum or an aluminumalloy. On the negative electrode side, the external terminal 14, theinternal terminal 15, and the connecting terminal 42 are made of copperor a copper alloy.

The insulating members 12 and 13 are fitted around the case-penetratinghole 11 c.

The first insulating member 12 is disposed on an inside of the lid 11 bto provide electrical insulation between the lid 11 b and the internalterminal 15. In the present embodiment, the first insulating member 12is composed of a resin member having required elasticity. Specifically,the first insulating member 12 is composed of a fluoropolymer. The firstinsulating member 12 ensures sufficient sealing of the case-penetratinghole 11 c. In the present embodiment, as illustrated in FIG. 2, thefirst insulating member 12 includes a base portion 12 a, a tubularportion 12 b, and a retaining portion 12 c. The base portion 12 a is aportion to be fitted on an inner surface of the lid 11 b. The tubularportion 12 b is a portion of the first insulating member 12 thatprotrudes from the base portion 12 a and is to be fitted onto the innercircumferential surface of the case-penetrating hole 11 c. The tubularportion 12 b has an internal diameter corresponding to the outerdiameter of the shaft portion 15 c so that a later-described shaftportion 15 c of the internal terminal 15 can be inserted therethrough.The retaining portion 12 c is provided to be the lower surface of thefirst insulating member 12. The retaining portion 12 c includes a recessthat corresponds to the shape of a later-described base portion 15 a ofthe internal terminal 15. The retaining portion 12 c is a portion of thefirst insulating member 12 on which the base portion 15 a is to bepositioned.

The second insulating member 13 is disposed on an outside of the lid 11b to provide electrical insulation between the lid 11 b and the externalterminal 14, and electrical insulation between the lid 11 b and theconnecting terminal 41. In the present embodiment, the second insulatingmember 13 is composed of a resin member. Specifically, the secondinsulating member 13 is composed of a polyamide resin. In thisembodiment, the lower surface of the second insulating member 13 isprovided with a protruding portion 13 a, as illustrated in FIG. 2. Theprotruding portion 13 a is fitted into the recess 11 b 1 of the lid 11b. The upper surface of the second insulating member 13 is provided witha recess 13 b, in which the positive electrode connecting terminal 41 isto be disposed, and a recess 13 c, in which the external terminal 14 isto be fitted. The recess 13 c, in which the external terminal 14 is tobe fitted, includes a through hole 13 d formed at a position thatcorresponds to the case-penetrating hole 11 c formed in the lid 11 b.The through hole 13 d has an internal diameter corresponding to theouter diameter of the shaft portion 15 c so that a later-described shaftportion 15 c of the internal terminal 15 can be inserted therethrough.

In the present embodiment, the insulating members 12 and 13 are composedof two component parts. However, the insulating members 12 and 13 arecomponent parts that provides electrical insulation between the lid 11b, the external terminal 14, and the internal terminal 15, and it shouldbe noted that the materials, the shapes, and the structures mentionedabove are merely examples. The insulating members 12 and 13 may becomposed of a single component part. Alternatively, the insulatingmembers 12 and 13 may be composed of a plurality of component parts,such as two or more component parts.

The connecting terminal 41 includes a flange portion 41 a and a shaftportion 41 b. The flange portion 41 a is positioned and fitted into therecess 13 b, which is provided in the second insulating member 13, whichis disposed on the outside of the lid 11 b. Accordingly, the flangeportion 41 a and the recess 13 b may have shapes corresponding to eachother. Note that the shaft portion 41 b is a part that serves as anoutput terminal.

In the present embodiment, as illustrated in FIG. 2, the externalterminal 14 includes a member-engaging hole 14 b and is stacked on anoutside of the lid 11 b so that the member-engaging hole 14 b and thecase-penetrating hole 11 c align with each other. The external terminal14 is a plate-shaped member disposed along the longitudinal axis of thelid 11 b. The external terminal 14 includes an attachment hole 14 a, towhich the connecting terminal 41 is attached, and a member-engaging hole14 b, through which the later-described shaft portion 15 c of theinternal terminal 15 is inserted. The member-engaging hole 14 b isformed at a position corresponding to the through hole 13 d of thesecond insulating member 13 under conditions where the external terminal14 is placed on the second insulating member 13. Thus, in the presentembodiment, the external terminal 14 is stacked on the outside of thelid 11 b with the second insulating member 13 interposed therebetween,because the lid 11 b is an electrically conductive member.

In the present embodiment, the internal terminal 15 includes a shaftportion 15 c and a fastening portion 15 c 1 and is stacked on the insideof the lid 11 b. The shaft portion 15 c is inserted through thecase-penetrating hole 11 c and the member-engaging hole 14 b from theinterior of the battery case 11. The fastening portion 15 c 1 is aportion of the shaft portion 15 c that is fastened to a circumferentialperiphery of the member-engaging hole 14 b by crushing a tip end of theshaft portion 15 c. As illustrated in FIGS. 1 and 2, the internalterminal 15 includes a base portion 15 a, an attachment piece 15 b, anda shaft portion 15 c. Of these, the base portion 15 a is fitted to thelid 11 b with the first insulating member 12 interposed therebetween.The details of the attachment piece 15 b have already been described andtherefore will not be repeated herein.

FIG. 3 is a partial plan view illustrating welded portions 50 formed inthe fastening portion 15 c 1 of the internal terminal 15 and theexternal terminal 14, according to the present embodiment. In FIG. 3,the welded portions are enlarged to facilitate understanding. In thepresent embodiment, as illustrated in FIGS. 2 and 3, the fasteningportion 15 c 1 and the external terminal 15 include welded portions 50that are seamlessly welded by using laser light along a weld line W thatis set across the periphery of the fastening portion 15 c 1. Herein, theterm “weld line W” refers to a scanning line of the laser beam in laserwelding. The weld line W may appear as a line through the center of theweld width of the welded portion 50, for example. In the presentembodiment, each of the welded portions 50 has a length K1 along theweld line W and a width K2 along a direction perpendicular to the weldline W, and the length K1 is greater than the width K2. In the presentembodiment, the length K1 is set to be approximately from 1.5 times to 4times the width K2. As a result, the welded portion 50 can bedistinguished from one that is formed by simply spot welding theboundary portion between the fastening portion 15 c 1 and the externalterminal 14.

In the present embodiment, the weld is formed along the weld line W thatis set across the periphery of the fastening portion 15 c 1. Therefore,each of the welded portions 50 is formed across the periphery of thefastening portion 15 c 1. In this case, the external terminal 14 issufficiently fused not only in an inside part of the fastening portion15 c 1 but also in an outside part of the fastening portion 15 c 1 sothat the fastening portion 15 c 1 and the external terminal 14 arewelded to each other. More specifically, the metal in the fasteningportion 15 c 1 that is fused by laser welding flows along the outersurface of the fastening portion 15 c 1, which is in an umbrella-likeshape, to the external terminal 14, and is mixed with the fused metal onthe external terminal 14 side, to effect welding. As a result, the weldarea can be made larger than, for example, the case where the boundaryportion between the fastening portion 15 c 1 and the external terminal14 is simply spot welded. Moreover, electrical continuity between theexternal terminal 14 and the fastening portion 15 c 1 of the internalterminal 15 can be ensured more reliably, and moreover, the electricalresistance between them can be further reduced. Therefore, the weld areacan be made larger in comparison with the case of spot welding, and as aresult, the internal resistance of the battery can be reduced. In orderto obtain such an advantageous effect, the welded portion 50 may be suchthat the length K1 along the weld line W is greater than the width K2along a direction perpendicular to the weld line W. For example, thelength K1 may be at least 1.5 times, more preferably at least 2 times,still more preferably at least 2.5 times the width K2. Such a weldedportion may be embodied by, for example, performing laser welding whileshifting the position to which laser is applied along the weld line W.

FIG. 4 is a cross-sectional view taken along line Iv-Iv in FIG. 3,showing a fastening portion 15 c 1. The shaft portion 15 c of theinternal terminal 15 is inserted through the case-penetrating hole 11 cof the lid 11 b and the member-engaging hole 14 b of the externalterminal 14. The tip end of the shaft portion 15 c is crushed andfastened to a circumferential periphery of the member-engaging hole 14 bthat is on the outside of the external terminal 14. The tip end of theshaft portion 15 c is deformed so as to spread into an umbrella-likeshape to form the fastening portion 15 c 1. As a result, the internalterminal 15 is secured so as to clamp the first insulating member 12,the lid 11 b, the second insulating member 13, and the external terminal14 between the base portion 15 a and the fastening portion 15 c 1.

Of the weld line W, a weld line L_(out) that is provided external to thefastening portion 15 c 1 may be set longer than a weld line L_(in) thatis provided internal to the fastening portion 15 c 1. For example, theweld line L_(out), which is provided external to the fastening portion15 c 1, may be set to be at least 2.5 times longer than the weld lineL_(in), which is provided internal to the fastening portion 15 c 1. Inother words, a portion of the welded portion 50 that is providedexternal to the fastening portion 15 c 1 may have a length along theweld line W at least 2.5 times longer than a portion of the weldedportion 50 that is provided internal to the fastening portion 15 c 1.Here, the distance from the center of the shaft portion 15 c of theinternal terminal 15 to the outer periphery of the fastening portion 15c 1 is defined as the distance r from the center of the fasteningportion 15 c 1 to the outer periphery of the fastening portion 15 c 1.The weld line L_(out), which is provided external to the fasteningportion 15 c 1, may be at least 0.25 times, preferably at least 0.3times, the distance R from the center of the fastening portion 15 c 1 tothe outer periphery thereof. On the other hand, the weld line L_(in),which is provided internal to the fastening portion 15 c 1, may be atleast 0.1 times, preferably at least 0.15 times, the distance R from thecenter of the fastening portion 15 c 1 to the outer periphery thereof.

It should be noted that, when the fastening portion 15 c 1 is in asubstantially circular shape centered about the center of the shaftportion 15 c of the internal terminal 15, the distance r from the centerof the fastening portion 15 c 1 to the outer periphery thereof can beapproximately the radius of the fastening portion 15 c 1. Thus, becausethe weld line L_(out) provided external to the fastening portion 15 c 1is set longer than the weld line L_(in) provided internal to thefastening portion 15 c 1, the weld area is increased further, and theelectrical resistance is reduced. Also, because the metal on theexternal terminal 14 side is fused in a greater amount in a regionexternal to the fastening portion 15 c 1, the thermal strain that mayoccur in the external terminal 14 is reduced, so that the quality of theexternal terminal 14 can be kept high.

As illustrated in FIG. 4, the welded portion 50 may be provided at onlyone location. It is also possible that two or more of the weldedportions 50 may be provided at respective locations. In that case, it isdesirable that the welded portions 50 be circumferentially spaced fromeach other. With the numbers of the welded portions being equal, such aconfiguration provides a larger weld area than the case where the weldedportions 50 are circumferentially overlapped with each other, andtherefore allows the electrical resistance to be kept even lower.

The region in which the external terminal 14 and the shaft portion 15 cof the internal terminal 15 are in contact with each other is under theforce exerted by fastening. In the present embodiment, the inner edge ofthe fastening portion 15 c 1 within the welded portion may be locatedradially outward of the member-engaging hole 14 b when viewed axiallyalong the shaft portion 15 c. With such a configuration, welding isunlikely to adversely affect the region that is fastened by thefastening force. As a result, the joining of the external terminal 14and the internal terminal 15 that is effected by fastening can be keptfirmly. From such viewpoints, the inner edge of the fastening portion ofthe welded portion is set to be located at at least 1.1 times, morepreferably at least 1.2 times, further outward than the radius of themember-engaging hole when viewed axially along the shaft portion.

In the foregoing embodiment, the weld line W extends in a radialdirection, and the center of the shaft portion 15 c is on an extensionline of the weld line W. However, the present disclosure is not limitedthereto. FIG. 5 is a partial plan view illustrating welded portions 50formed in the external terminal and the fastening portion of theinternal terminal, according to a modified embodiment of the presentdisclosure. As illustrated in FIG. 5, the weld line W may be set to beoffset from a line along a radial direction through the center of theshaft portion 15 c in a direction perpendicular to the radial direction.In addition, the weld line W is not limited to a straight line but maybe set to be a curved line.

In the foregoing embodiment, the welded portions 50 are providedsymmetrically. However, the present disclosure is not limited thereto.As illustrated in FIG. 5, the numbers and the locations of the weldedportions 50 may be asymmetrical.

In the foregoing embodiment, the external terminal 14 and the internalterminal 15 are provided on the lid 11 b. However, the presentdisclosure is not limited thereto, and the external terminal 14 and theinternal terminal 15 may be provided on the battery case 11.

The external terminal 14 and the internal terminal 15 may be made ofdissimilar materials. For example, in secondary batteries that have acharge potential such that the open circuit voltage of the positiveelectrode and the negative electrode is about 4 V, the electrodeterminal on the positive electrode uses aluminum or an aluminum alloythat can withstand a required voltage. In such cases, dissimilarmaterials may be used for the external terminal 14 and the internalterminal 15. For example, in the embodiment shown in FIGS. 2 and 3, theinternal terminal 15 of the positive electrode that includes the shaftportion 15 c, which needs to be crushed, may use aluminum, which isrelatively a soft material. On the other hand, the external terminal 14may use an aluminum alloy that shows excellent corrosion resistance andstrength.

A method of manufacturing a battery that includes such a welded portion50 will be described below. In the method of manufacturing a batteryherein, a battery case 11 including a case-penetrating hole 11 c, anexternal terminal 14 including a member-engaging hole 14 b, and aninternal terminal 15 including a shaft portion 15 c are prepared.

Next, the battery case 11, the external terminal 14, and the internalterminal 15 are assembled together. In this step, the external terminal14 is placed on an outside of the battery case 11, the internal terminal15 is placed on an inside of the battery case 11, and the shaft portion15 c is inserted through the case-penetrating hole 11 c and themember-engaging hole 14 b. In the preferred embodiment, the firstinsulating member 12 is internal terminal between the battery case 11and the internal terminal 15. The second insulating member 13 isinterposed between the battery case 11 and the external terminal 14.

Specifically, the external terminal 14 is placed on the outside of thelid 11 b so that the second insulating member 13 is interposedtherebetween and also the positions of the case-penetrating hole 11 cand the member-engaging hole 14 b are aligned with each other. Next, theinternal terminal 15 is placed on the inside of the lid 11 b so that thefirst insulating member 12 is interposed therebetween and the shaftportion 15 c of the internal terminal 15 is inserted through thecase-penetrating hole 11 c and the member-engaging hole 14 b.

Subsequently, a tip end of the shaft portion 15 c is crushed andfastened to the circumferential periphery of the member-engaging hole 14b that is on the outside of the external terminal 14, to form thefastening portion 15 c 1. Thus, the internal terminal 15 is secured soas to clamp the first insulating member 12, the lid 11 b, the secondinsulating member 13, and the external terminal 14 between the baseportion 15 a and the fastening portion 15 c 1.

Then, the fastening portion 15 c 1 and the external terminal 14 areseamlessly laser welded along the weld line W that is set so as toextend across the periphery of the fastening portion 15 c 1 along theouter surface of the fastening portion 15 c 1. In such a configuration,the fastening portion 15 c 1 is in an umbrella-like shape. Therefore,the metal of the fastening portion 15 c 1 that is fused by the laserlight flows toward the external terminal 14. Also, the external terminal14 is fused by the laser light in a region external to the fasteningportion 15 c 1, so the metal of the fastening portion 15 c 1 is mixedand welded with the metal of the external terminal 14. As a result, theweld area is increased and the electrical resistance is reduced, so thatthe internal resistance of the battery 10 is reduced.

The welded portion may be provided at either one location or two or morelocations. When a plurality of locations are to be welded by laserlight, a plurality of welded portions may be provided so as to be spacedfrom each other along a circumferential direction of the fasteningportion 15 c 1. In that case, for example, in the step of laser weldingthe fastening portion 15 c 1 and the external terminal 14 to each other,weld lines W may be set at two or more locations that are spaced along acircumferential direction of the fastening portion 15 c 1, and thefastening portion 15 c 1 and the external terminal 14 may be laserwelded to each other along the plurality of weld lines W. When aplurality of welded portions are formed so as to be spaced from eachother along a circumferential direction of the fastening portion 15 c 1in this way, the occurrence of spatter resulting from the heat input inwelding can be reduced, and accordingly, weld defects can be reduced.

In the step of seamlessly laser welding the fastening portion 15 c 1 andthe external terminal 14, a region that is to be laser welded may be setto be at least 2.5 times longer in a region external to the fasteningportion 15 c 1 than in a region internal to the fastening portion 15 c1. In this case, the weld line L_(out) that is provided external to thefastening portion 15 c 1 may be set at least 2.5 times longer than theweld line L_(in) that is provided internal to the fastening portion 15 c1. When the external terminal 14 and the fastening portion 15 c 1 aremade of dissimilar materials, their thermal expansion coefficients maybe different. When that is the case, as the welded portion 50 fused bythe laser light undergoes heat shrinkage according to a temperaturedrop, a thermal stress resulting from the difference in thermalexpansion occurs between the external terminal 14 and the welded portion50. When the region that is to be laser welded is set to be at least 2.5times longer in a portion external to the fastening portion 15 c 1 thanthat in a portion internal to the fastening portion 15 c 1 as describedabove, it means that the external terminal 14 is fused in a wider area.This serves to lessen the temperature dropping rate of the weldedportion 50. Therefore, even if the welded portion 50 undergoes heatshrinkage, the thermal stress produced in and around the welded portion50 is kept small.

In addition, in the step of laser welding the fastening portion 15 c 1and the external terminal 14 to each other, the fastening portion 15 c 1and the external terminal 14 are welded so that the welded portion 50does not extend into the inside of the member-engaging hole 14 whenviewed axially along the shaft portion 15 c. In other words, the inneredge of the fastening portion of the welded portion is set to be locatedat at least 1.1 times further outward than the radius of themember-engaging hole when viewed axially along the shaft portion. Withsuch an embodiment, laser welding is unlikely to adversely affect theregion of the fastening portion 15 c 1 that is under a fastening force.As a result, the joining of the external terminal 14 and the internalterminal 15 that is effected by fastening is kept firmly.

Although various embodiments of the battery and the method ofmanufacturing the battery have been described hereinabove according tothe present disclosure, it should be noted that, unless specificallystated otherwise, the embodiments and the examples described herein donot limit the scope of the present invention.

What is claimed is:
 1. A battery comprising: a battery case; an externalterminal; and an internal terminal, wherein: the battery case includes acase-penetrating hole; the external terminal includes a member-engaginghole and is stacked on an outside of the battery case so that themember-engaging hole and the case-penetrating hole align with eachother; the internal terminal is stacked on an inside of the batterycase; and the internal terminal includes: a shaft portion insertedthrough the case-penetrating hole and the member-engaging hole from aninterior of the battery; and a fastening portion fastened to acircumferential periphery of the member-engaging hole at a tip end ofthe shaft portion; the fastening portion and the external terminalinclude a welded portion welded along a weld line set across a peripheryof the fastening portion; and the welded portion has a length K1 alongthe weld line and a width K2 along a direction perpendicular to the weldline, and the length K1 is at least 1.5 times longer than the width K2.2. The battery according to claim 1, wherein a portion of the weldedportion that is provided external to the fastening portion has a lengthalong the weld line at least 2.5 times longer than a portion of thewelded portion that is provided internal to the fastening portion. 3.The battery according to claim 1, wherein: the at least one weldedportion includes at least two or more of the welded portions; andadjacent ones of the welded portions are circumferentially spaced fromeach other.
 4. The battery according to claim 1, wherein the weldedportion includes an inner edge of the fastening portion, the inner edgebeing located radially outward of the member-engaging hole when viewedaxially along the shaft portion.
 5. A method of manufacturing a battery,comprising the steps of; preparing a battery case including acase-penetrating hole; preparing an external terminal including amember-engaging hole; preparing an internal terminal including a shaftportion; assembling the battery case, the external terminal, and theinternal terminal together so that the external terminal is stacked onan outside of the battery case, the internal terminal is stacked on aninside of the battery case, and the shaft portion is inserted throughthe case-penetrating hole and the member-engaging hole; forming afastening portion by crushing a tip end of the shaft portion andfastening the tip end of the shaft portion to a circumferentialperiphery of the member-engaging hole on an outside of the externalterminal; and laser welding the fastening portion and the externalterminal seamlessly along at least one weld line that is set so as toextend across a periphery of the fastening portion along an outersurface of the fastening portion.
 6. The method according to claim 5,wherein, in the step of laser welding, a region that is to be laserwelded is set to be at least 2.5 times longer in a region external tothe fastening portion than in a region internal to the fasteningportion.
 7. The method according to claim 5, wherein, in the step oflaser welding, the at least one weld line is set at two or morelocations of the fastening portion that are circumferentially spacedfrom each other, the fastening portion and the external terminal arelaser welded together along a plurality of the weld lines, and aplurality of welded portions that are circumferentially spaced from eachother are formed by the laser welding.
 8. The method according to claim5, wherein, in the step of laser welding, the welded portion does notextend into an inside of the member-engaging hole when viewed axiallyalong the shaft portion.